The present invention relates to the carrying out of a fast and strongly exothermic catalytic reaction between two or more gaseous compounds. A typical example thereof is the manufacturing of methane from a mixture of CO and H.sub.2 according to the overall stoichiometry: EQU CO+3H.sub.2 .revreaction.CH.sub.4 +H.sub.2 O
or the manufacturing of alcohols, particularly methanol, according to the overall stoichiometry: EQU CO+2H.sub.2 .revreaction.CH.sub.3 OH
or otherwise the manufacturing of hydrocarbons heavier than methane or alcohols heavier than methanol.
These reactions are so strongly exothermic (the adiabatic temperature rise, when synthesizing methane, is about 17.degree. C. per each 1% of conversion) that in most cases they require the use of a diluent, associated or not with a thermal exchange through the wall of the reactor. Several processes have been designed which make use, as diluent, either of the output gaseous mixture which is then partially recycled, with or without steam injection, or of a liquid, for example a hydrocarbon, which, under the operating conditions, can remove the heat by sensible heat and evaporation.
A high recycle rate of the liquid and the condensed vapor ensures the thermal stability of the reactor.
In the processes operated with a liquid, the catalyst is normally used either as a suspension of fine particles or as unmoved particles of a fixed or ebullated bed.
It is important that the catalyst be immersed in the liquid to ensure a good liquid-solid contact everywhere, thereby avoiding the formation of a dry zone in the reactor, which zone could be responsible for an insufficient thermal stability; very high temperatures can be attained in that dry zone, since the reaction can take place entirely in the gas phase therein. A number of techniques have been proposed, wherein a continuous liquid phase is circulated upwardly, the catalyst being used as a suspension, as an ebullated bed or as a fixed or moving bed. These techniques have however serious disadvantages: substantial attrition of the catalyst takes place, due to the displacement of the catalyst particles, even with a so-called fixed bed; fine catalyst particles can be carried away from the reaction zone, resulting in racing of the reaction in the separators, the exchangers or at any other part of the plant; finally the productivity of the catalyst bed is relatively low.
A technique using a downflow stream (trickle flow) of gas and liquid has been proposed (U.S. Pat. No. 2,167,004). This technique has not been used on an industrial scale, since, in that case, the reactants flow through the reactor in such a way that the gas phase is the continuous phase and the liquid flows as thin streams or drops. This type of flowing leads easily to the formation of dry zones, resulting in thermal instability.
Thermal instability can be sometimes tolerated by the catalyst for a certain time, when it is weak. However it unavoidably results in a shortening of the catalyst life.